CA2126274A1 - Deep core radial noise suppression treatment for jet aircraft engine - Google Patents

Abstract

DEEP CORE RADIAL NOISE SUPPRESSION TREATMENT
FOR JET AIRCRAFT ENGINE

Abstract of the Disclosure A tubular component such as an exhaust shroud is provided for use in a noise suppression system for an aircraft jet engine, the tubular component providing an outlet passage for jet engine produced exhaust gases having turbo-machinery produced sound energy superimposed thereon, the tubular component having an outer structural shell with a tubular axis and an acoustic liner supported within the structural shell formed of a tubular honeycomb metallic core, the honeycomb core being formed of thin metallic strips joined into a welded honeycomb arrangement of contiguous hexagonal cells, Each of the cells has a longitudinal axis extending perpendicular to the shell tubular axis, each shell being of depth of at least one inch and of a cross-sectional size from wall-to-wall of about 3/8 to 1/2 inch.

Description

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DEEP CORE RADIAL I~IOISE SUPPRESSION TREATMEI~T
FOR .3ET AlRCiRAFT NGINE

BackgroLlnd Ot Th~ Dlsclosur~
This disclosure relates to a tubular compon~nt, such as an exhaust shroud, formsd as a part of a noise suppression system for an aircraft jet el1gine. The noise produced by a jet engine is composed basically of: ~a) a broadiband r~nergy related io the jet exhaust velocity, and (b) a narrowband tone energy produced by the turbo-machinery of 5 the jst engine ~self. If an exhaust shroud extending aft of the engine can be made to absorb and dissipate the low frequency energy produced by the Jet engin~, then a si~iniïïcant portion of the o~erall noise prociuc~d by an aircraft Jet engine can be eliminated.

The usc of a sound absorption material within an exhaust shroud is well known, ~s exemplified in ths followin~ United States Patents: 4,909,346 and 5,060,471.
'''' A typical method of providing sound absorption material is the use o~ a honeycomb panel. Any sound absorption materlal ussd in a Jat en~in6 nois~ supprassion syst~m must be c~pabb of withstandin~ th8 hi~h temperatures ancountered in ths enyinB
! ~, exhau~t and thus must be made of metai, the preferred metal beiny stainless steel.
15 Stalnless steel honsycomb panals are typically producad wlth a honayeomb cora wi~h a pianar materiai coverln~ one or both ~ides. When usin~ such planar honeycomb panels it ts ns¢essa~y to carve them Inta ~rcuate portions to f t inside the usual tubular exhaust `

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shroud. The problem is that this method produces unequal individual cell sizes and cell alignments as measured with reference to the exhaust shroud tubular axis.

The use of honeycomb materiai that has irregular cell heights and cell ali~nments reduces the effectiYeness of sound absorption. Absorption of a relativeiy low frequency 5 band is raquired to effcctively dissipate the sound enar0y tone prociuced by a Jet engine.
In other wordsl th~ sound absorption characteristics of pr~vioLsly used hon~ycomb sounci absorption material has not maximized the noise reduc~on potential of a noise reduction system for use with a Jet snglne.

A method of manufacturtng honeycomb core material tha~ can i~ used in provided 10 honoycomb sound ~bsorptive material to practice the inventi~ of this disclosure is described In Unl~ad States Patent 5~064l493 Issu8d Nov~mber 12,1991. Patent 5,064,493 Is Incorporated harain by reference.

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Summary C~ The Invention This invention pertains to a tubular component, such as an exhaust shroud used in a system for noise abatement o~ a J~t aircraft en~ine. More particularly, the invention relatr~s to an ~xhaust shroud used in a Jet engine noise suppression system that provides a tubular component through which thrust producing Jet ~3ngine exhaust gases pass.
5 ~hese Jet engins ~ases inh~rently have a low frequency band of sound ensrgy produced by the Jet engine its~H. If this low fr~quenc~ sound produced energy is not absorbed in so~ne way, it becomes a si~nificant component of the overall noise ~enerated by the engine. By providing a sound absorption material within the tubular component (such as an exhaust shroud) capable of absorbing the low frequency sound produced energyl the 10 tot~l r~suitant nolse of the Jet r~n~in0 can be reduced.

The inclusion of sound absorption material in an e~haust shreud is a known technlque ss revealad such ~s in United Stat~s Patent Numbers 4,9~9,346 and 5,060,471.
An effec~ive and a preferred type of sound absorption material is a panal h~ving a honeycomb cora formad of thin rnetal strips bent and welded together to ~orm contiguous 15 i~neycomb calls. Hon0ycomb panels are typically formed In flat sheefs. A honeycomb co e c~n ~ b~nt into a curve if the depth of the honeycomb core is relatively small, such . as one inch or less. However, n has been learned that the most effective sound absorption system employin~ a honeycomb core mat~rial requires honeycomb cells o~
d~pth ~reater than one inch, as much as five or six inchss, w th a depUh of two or thre~
20 Inohes b~in~ typical. The previous efforts to provide honeycomb sound absorptTon material w'th sl~nfflcar~t depths, such as mor0 than one inch, and particu!arly two or three ~ 2~ ~27~

inches, have employsd flat honeycomb panels of this depth that ar~ machined, after the panels are manufac~ured, to required circumfcrantial contours to fit within a tubular exhaust shroud. This technique has met with less than c~mplete sucoess sincs such arrar gement provldes a honeycomb sound absorption material wherein the honeycomb 5 cells are of an irregular configuration.

The present Invention solves the problem of th~ known type of deep cell honeycomb sound absorption systems for use in exhaust shrouds by providin~ an acoustic liner formed of a honeycornb metallic core with contiguous~ hexagonal honeycomb CQIIS arranged such that th~ cells each have a long hudinal a~is that ~xtends 10 perpendicular to the tubular axis of the exhaust shroud. Each oell is symm~trical with respect to the other cells in the sound absorption system. Ths typical depth of the cells, wh c)~ depands upon the sound ~requency bein~ absorbed, is two or thrae inches but in some applications may be five or six Inchas. ~he typical dimension of the cells measured from sidewall to sid~wall at the outer circumferential periphery of the tubular sound 15 absorptian mat~rial is abolJt 3/8 inch to 1/2 inch.

In ~ pref~rred arran~ement of th~ InvenUon, an acoustical liner is providad for support within a structural shell formin~ an exhaust shroud, the acousUcal liner bein~
forrned wiU~ a hon~ycomb metal cora of d~pth ~xcee~in~ one inch and with hexa~onal cell sizas of about 3/8 in~h to 1 inch and inclu~in~ a p~rforated umer skin affixed to th0 20 honeycomb metal core. The perforated skin provides sound communication witnin th~
Intenor of thc h~xagonal cores of the honeycornb core but, at tha same timeJ adds 212627~
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strer~th and rigidity lo the acoustic liner and reduces the drag on ie~ exhaust ~ases ; ~;
pass ng through the exhaust shroud.

A better understandin~ of the invention will be had by reference to the following :
desc~iption of the prefetred embodiment and ths claims, taken in conjunction with the .:
5 aHachr~d drawinos.

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D~scrlptlon Ot Thc Orawin~s Figure 1 is an exploded view of a typical sound absorption system for use in coryunction with a turbofan aircraft 0ngine, a major component of the system being the e~aust shroud component to which this invention pertains.

Fliure 2 Is an illustration of the prlor art showing how relatively thick honeycomb 5 panels, manufactured in the usual planar configuration, can i~ contoured and thsn assembled circumferentially in a process of manufacturing a tubular acoustic iiner for use h ~n exhaust shroud.

Fi~ure 3 is a fragmcntary YieW 0~ the prior art illustrated in i~i~ure 2 showing a segrnent of a honcycomb ~ore liner that can bc used as an acoustic liner in an sxhaust 10 shroud of the type ~ormed of a btock of planar hon~ycor~b cor~ and showin0 that the configuration of the c~lls vary in len~th and shape.

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Fi~ur~ 4 Is a partial ctoss-s~ctional viraw diagrammat;caliy iliustrating ~h~ cells of a honeycomb core aooustic liner arran~ed according to the pnnciples of ~his invention wherein ~ach of th~ c~lls of the aooustic liner has a long~udinal axis tha~ is perpendicular 1S tQ the exhaust shroud tubular axis.

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Figure 5 is a diagrammatic illus~ration of a single cell of a honeycomb core acoustic tincr illustrating the ~n~ral appearance of a cell, however, in this iilus~ration tha dimensions are not in proportion, in that the illustration shows the width of the ~ypical cell out of proportion to the typical tength. ~ .

Figure 6 is a fragmentary view of an acoustic liner as employed in an exhaust shroud as taken alon~i th~ lin~ 6-6 of hgurr~ 1. Figur~ 6 shows a short length s~o~ion of an acoustic liner that employs a perforated inner skin and with the outer skin of the acoustic liner bein~ b~oken away to show the configura~ion of the honeycomb cells.
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Figure 7 is a diagrammatic illustration of a cross-section of a cell showin~ theopposed sid0walls and innsr and out~r skins, the inner skin being perforated to provide an entry for sound into tho call and showln~ sound waves as they travel within the c~

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Descrlptlon Ot Th~ Pre~err~d Em~odlment Figur0 1 is an illustration of one method of providing sound abatement for a tur~ofan aircraft en~ine. A typical turbofan engine is indicated by the numeral 10 having an exhaust end 12. The en~ine 10 functions by exhausting gases at exhaust end 12 at thrust producing velocitles. Jet aircraft en~inss are extremely effective for producing 5 thr~st, however, the heated exhaust gases passin~ ou~ the exhaust end produce hi~h levels of noise, and the aircraft industry has been workin~ to abate the noise produced by engines.

The noise produced by the exhaust ~ases passin~ out exhaust end 12 of a jet angine 10 are composed basically of, first, a low frequency enargy relating to the exhaust 10 Qas velo~y and, ssconcl, to a narrowband tone enargy produc~d by the turbo-machinary of ~e l~t 0n~in~ itself. mis inventiorl i~ conc~rn0d primarily with the low fr~quency ener~y produced by the exhaust gas of the Jet engines.

FiSur~ 1 shows compon9nts that can ~e errployed to help reduce the noise ~ -~eneratsd by an engine, including an internal flow mixer 14, an exhaust nozzle 16, and i -1~ an exhaust shroud 18. The sxhaust shroud is the final element ~hrou~h which ths Jet ~ngine thrust producin~ ~ases pass bafore exiting to the atmosphere. txhaust shroud 18 includes an acoustio liner 20 desi0ned to absorb sound of tha exhaust ~as~s and to absorb the band tone cnar~y produced by the turb~machin~ry of jet engin~ 10. This inveintton Is concarn~d ~ntiraly with th~ ~xhaust shroud 18 and i~tcularly the acoustic . .

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liner 20 therein, the other components of Figur~ 1 being illustrated merely to indicate a typical environment in whic'n an exhaust shfoud having acoustic liner 20 therein can be employed.

The acoustic liner 20 can be formed in various ways, however, one method which has proven satisfactory and which is deemed to bs the preferred method of providin~
acoustic lin~r 20 employs the us~ of a linsr made witi~ a hon~ycornb metallic cor~. The use of honeycomb panels is well known in ~he aircraft industly and the use of a honeycomb core has been previously employed in connection with ex'naust shrouds in an effort to reduce noise. Figures 2 and 3 are illustrative of ~e prior art and show 10 m~thods wh~reby flat panels of honeycomb corc material can b~ employed in manufacturin~ a honeycomb core. Fl~ure 2 shows threc planar honeycomb deep c~
panels 22A, 22B and 22C arran~ed in an olnline 24 of a tubular acoustic linar as can be ~rnployed in lin~r 20 of F0ur~ outline 24 sup~rimposed ovar the planar honsycomb panels 22A, 22B and 22C illustrates how such panels must b~ ~haped so that 15 they can b~ assembled to~ether in th~ formation of a tubular acoustic liner. Figurs 2 shows only Ulre0 ~f the planar honeycomb panels, it being appar~t that mors than these U~r~e ar~ requtred to provide a comple~e circumferantial tubular acoustic liner.

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Fi~ure 3 is another illustration of t'n~ prior art showing the honeycomb material that is obtain~d from shapin~ a planar honeycomb pan~l 22B. The panel includes an inner 20 skin 26 and outer skin 28 with a honeycomb core therebetween definin~ a plural~y of individual honeycomb cells 30 It Is app~rant from F~ure 3 that an acoustic liner formed 21~27~

in this meth~cl provides honeycomb c~lls 30 that are irre~ular in configuration. The honeycomb cells vary in depth and cross-sectional shape and, therefore, the cells are inherently tuned to absorb different sound frequencies. it can be seen from Figures 2 and 3 that providing a honeycomb of this construction formed of planar honeycomb 5 panels does not iend itseH to the formation of an acoustic liner capable of effectivr~ly absorbins a narrow band of low frequency ener~y.

The Improved acoustic liner of this invention is illustrated in Fi~ures 4 throu~h 7.
The basic concept of the improved liner is the employment of a honeycomb core that is cor~truct~d so that ~ach ce71 of thc cor~ is arranged radially about the ~ubular a~is of a 10 tubular compon~nt of a Jat aircraft en~in~ sound abat~ment system, such as the exhaust shroud 18 of Figure 1. A tubular ax~s of such twbular cornponent is illustrated by the numer~ 32 in Figurss 4, 5 and 6. Each of thc c811s 34 of the improved acoustic liner 20 has an ima~jinary lon~udinal axis 38 ~ nciin~ c~ntrally within the intsrior of ~ach ~11 and ext0nding in the diraction of the length thereof. As shown in figura 4, the longitudinal 15 axis o~ each cel. 34 is arranged to be p~rpendicular to tubular axis 32 of the tubular odlaust shroud. In this way each c81134 iS uniform in its size, includinçj i~s width and length, and In its orientation relativo to the exhaust ~ases passing throu~h the tubular exhaust shroud. 1~)9 sound absorption characteristics of the liner can ba car~fully tuned to a frequency band whlch most e~fectively absorbs the low frequency tone ener~y 20 produc~d by aJet engine.

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Figure 5 is an isometric diagrammatic representation of a single cell 34. Cell 34 ~:
h~s hexagonal sidewa~ls and is contiguous to adjac~3nt hexagonal c~lls. Cell 34 has ~
len~th 40 that is relatively lon~ compared to its width. Len~th 40 is at least one inch or greater and as much as six inches, with the typlcal langth being about two to three inches 5 as required for effective sound absorption of the low frequency sound produced by the typ cal Jet ~n~ine. The width of the cell as mcasured from opposed hexagonal sid~walls, ~K~ated by the numeral 42, is typicall~f 3/8 inch to 1 inch. Thus, the cells are relatively srnall in cross-section compared to their length 40.
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Manufacturing honeycomb material for a curvsd configuration as requirsd to provide a tubular core of a depth of one inch or more as requir~d for the improved stic linsr 36 can be accomplish~d utilizing the technique as illustrated in United States Patent No. 5,0~,493 Tssu~d Nov~rnber 12,1991 cntitled ~Method Of Producing Curved ~ ~ .
Honeycomb Core Material Havin~ C:rimps In One Edg~

Figure 6 illustrates a fragmentary section of the improYed tubular acoustic liner 20 as would be employed In an sxhaust shroud 18, sueh as tak~n along the lin~ 6~ of F~uro 1. llle tubular liner is formed of the honeycomb rnetallic COte having the muitipticKy of cells 3~ rein w~h an outer skin 44 and an inner skin 46. l~le outer skin 44 ~ preferably impervious, or w-~hout openin~s therethrough, whereas inner skin 46 is preferabiy perforated as illustrated. ~a p~rforated inner skin 46 allows sound cornmunication with th~ interior o~ each cell 30, whils outer skin 44 prevld0s a reflective s~Jrfac~ within 0ach c~ll. -2~2627~

Figure 7 is a cross-sectional diagramma~ic illustration of a typical cell 30 showing inner skin 4~, outer skin 44 and with cell sidewalls 48. The sidewalls 48 define celi 30, sidewalls 48 being hexagonally arranged as shown in Fi~ures 5 and ~. As previously st~ted, inner skin 46 is perforated providin~ an openin~ 5t) that communicatss with the interior of cell 30. Sound waves characterized by the low frequency tone ener~y ; .
producad by the jet engines are indicated by ths numeral 52. These sound wav~s pass th-ough openin~ 50 Into tne interior of cell 30 where they are reflected by outer skin 44, the reflected waves being indic~ted by the num0ral 54. The capture of the sound energy ~in the individual cells serve to dissipate the sound energy, and by the ~aometrical arrangement of the cells the dimensions can be selected to match the tonal energy to be absorbed. Thus, h~ure 7 dia~rammatically illustrates the manner in which low frequency tone enerQy produced sound waves 52 are ~ffectively absorbed by oells 30 so that a sui~stanUal portion of ~e tone energy of wave 52 is absorbsd, as indicatad by tha dissipat~d en~r~y 56.

me clairns and the specificaUon describe th~ invenUon presented and the terms ~at ar~ employed In the claims draw th~ir rn~anin~ from Ule us~ of such lsrms in th~ :
specification. ll~e same terms ~mployed in the prior art may be i~oader in meanin~ than speci~çally cmployed herein. Whenever th~r~ is a quesUon between the broader definition of such terms us~ci In the prior art and the mora specific us~ of th~ t~rms herein, th~
more specifie meanin~ is meant.
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While the invention has been described with a certain degree of particularity, it is mar~fest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. : :
~t is understood that the invention is not lim~ed to the embodirnents s~ forth herein for pl rposes of exernplification, but is to be limited only by the scope of the attached claim ~ :.
or daims, includin0 tha full range of equivalency to which each element thereof is entitled.

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Claims (3)

1. For use in a noise suppression system for a jet aircraft engine having a tubular component through which thrust producing jet engine exhaust gases pass, the gases having superimposed thereon turbo-machinery produced sound energy, the component comprising:
an outer structural shell having a tubular axis; and an acoustic liner supported within said structural shell comprised, at least in part of a tubular honeycomb metallic core formed of a honeycomb of thin metalstrips joined into a honeycomb arrangement of contiguous hexagonal cells, substantially all such cells each having a longitudinal axis extending substantially perpendicular to said shell tubular axis, each cell being of a depth measured parallel said cell longitudinal axis of at least 1 inch, each cell having an inner end in the direction of said structural shell tubular axis and an opposite, outer end, each cell being divergently tapered form said inner to said outer end.

2. A noise suppression component for jet aircraft engine noise suppression according to claim 1 wherein said liner is formed of hexagonally shaped cells, the sides thereof being spaced about 3/8 inch t 1/2 inch.

3. A noise suppression component for jet aircraft engine noise suppression according to claim 1 wherein said acoustic liner includes a perforated inner skin secured to said honeycomb metallic core.